In recent years, there has been increasing demands for rapid circuit signal processing, high frequency, high performance, miniaturization, and ultra-slimness of electronic elements in digital devices for various applications, such as automotive vehicles, mobiles, displays, and information electronics. Flexibility is further required in flexible electronic devices. In response to these demands, efforts have been made, for example, to highly integrate circuits in semiconductor devices. Thus, there is a tendency to hybridize dielectric noise-radiating active elements with passive elements. As a result of this hybridization, capacitive coupling and inductive coupling enhance cross talk, radiated noises interfere with each other, and heat is released, resulting in frequent malfunction of devices without normal operation. In some cases, noises in the near-field region, i.e., the distance between the radiation source and noise attenuation material is lower than the wavelength of the radiation (λ/2π), may interfere with each other. This interference often affects the operation of an external device.
Measures against noises and interference of electromagnetic waves in rapid-processing, high-performance, high-integration electromagnetic devices, particularly, measures against noises in the band of 100 MHz to 20 GHz, include many techniques, such as shielding, grounding, and installation of low-pass filters.
The typical shielding techniques include electrostatic shielding and magnetic shielding. The electrostatic shielding is associated with the use of an electrically conductive metal case (such as an aluminum or copper case), or a wire mesh or screen to block a far-field electric field radiated from the outside, while allowing free passage to magnetic fields. The magnetic shielding is associated with the use of a magnetic metal case with high magnetic permeability to shield a far-field magnetic field entering from or emitted to the outside. That is, the conventional shielding techniques are associated with the use of shielding materials capable of reflecting or absorbing far-field electromagnetic waves to block the far-field electromagnetic waves entering or exiting at the distance between the radiation source and shielding material greater than λ/2π. When noises are shielded by far-field shielding techniques, some of them are reflected and some are absorbed. The reflected noises and the absorbed noises coexist and are thus amplified. Accordingly, the shielding techniques cannot be used to suppress interference of near-field noises emitted from internal IC chips and circuits of devices. An excessively high reflectance of noises may also negatively affect peripheral circuits and an excessively high absorbance of noises may lead to signal reduction. Therefore, grounding or filtering techniques are employed to suppress interference of near-field noises.
The grounding techniques include frame grounding and signal grounding. According to the frame grounding, a metal case and a sash are grounded to the earth. According to the signal grounding, a metal case and a sash are grounded to a ground circuit board. The grounding techniques are designed to keep the impedance of earth circuits as low as possible and to minimize the ground loop area.
Finally, the EMI filtering techniques use combinations of passive elements such as inductance components and capacitance components. According to the EMI filtering techniques, noises are typically attenuated by using a power filter designed to withstand high voltage and current of 30 MHz or less and a signaling filter used in a current signaling system at 30 MHz or more.
However, the use of these elements is not suitable as an urgent measure against noises in devices with short life cycles because mounting spaces for the elements are required and miniaturization and slimness of the elements should be considered from the design stage. Inductance elements are also still very insufficient for use in the radio-frequency (RF) or semi-microwave band due to their low-frequency characteristics of the real component of permeability.
With the trend toward miniaturization of semiconductor devices and digital devices, there is a growing demand for ultra-slim/ultra-thin films and devices including the films for effectively controlling near-field noises and heat generated from adjacent noise sources inside an electronic device used in the RF or semi-microwave band. In view of this situation, sheets and films using ferrite or soft magnetic materials have been used to suppress electromagnetic waves. Such methods are based on noise reduction effect derived from magnetic loss. Insufficient permeability with increasing frequency limits ultra-slimness/ultra-thinness and lowers the frequency characteristics of the imaginary component of permeability, leading to a negligible noise reduction effect. Elements such as coils and filters may be used in the frequency bands lower than and higher than several tens of MHz to several hundreds of MHz. However, there are no elements that are convenient to use as measures against noises in the RF band. Even though some passive elements are known to be suitable as measures against noises, enormous costs are incurred, for example, in changing the design of substrates.
In order to solve such problems, there is a need for circuit devices and light-weight and thin films as measures for noise reduction/heat dissipation that can be applied to a wider range of frequency than magnetic sheets and are effective in noise reduction and heat dissipation even in the form of thin films. Particularly, methods for noise attenuation using a number of passive elements in devices such as semiconductor devices, smart phones, and flexible displays, which require smaller size and thickness and lighter weight, have difficulties in mounting the passive elements and in achieving slimness and heat dissipation due to the limited sizes of the passive elements. Under these circumstances, there is an urgent need to develop a noise attenuation film that is advantageous in nanodevice fabrication and high heat dissipation, and an electronic device including the film.